Terminology

Allotropes
Some elements exist in several different structural forms, these are called allotropes.

For more information on Murray Robertson’s image see Uses/Interesting Facts below.

Molybdenum

Discovery date	1781
Discovered by	P.J. Hjelm
Origin of the name	The name is derived from the Greek 'molybdos' meaning lead.
Allotropes	-

95.96

Fact Box Terminology

Group
Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

Period
Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.

Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp, principal, diffuse, and fundamental.

Atomic Number
The number of protons in the nucleus.

Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.

Electron Configuration
The arrangements of electrons above the last (closed shell) noble gas.

Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Melting Point (^oC)
The temperature at which the solid-liquid phase change occurs.

Melting Point (K)
The temperature at which the solid-liquid phase change occurs.

Melting Point (^oF)
The temperature at which the solid-liquid phase change occurs.

Boiling Point (^oC)
The temperature at which the liquid-gas phase change occurs.

Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.

Boiling Point (^oF)
The temperature at which the liquid-gas phase change occurs.

Sublimation
Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.

Density (kgm^-3)
Density is the weight of a substance that would fill 1 m³ (at 298 K unless otherwise stated).

Relative Atomic Mass
The mass of an atom relative to that of Carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists the value given is the abundance weighted average.

Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. ¹²C has 6 protons and 6 neutrons and ¹³C has 6 protons and 7 neutrons).

CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact Box

Group	6	Melting point	2622 ^oC, 4751.6 ^oF, 2895.15 K
Period	5	Boiling point	4639 ^oC, 8382.2 ^oF, 4912.15 K
Block	d	Density (kg m^-3)	10222
Atomic number	42	Relative atomic mass	95.96
State at room temperature	Solid	Key isotopes	⁹⁵Mo, ⁹⁶Mo, ⁹⁸Mo
Electron configuration	[Kr] 4d⁵5s¹	CAS number	7439-98-7
ChemSpider ID	22374	ChemSpider is a free chemical structure database

Interesting Facts terminology

Image Explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.

Natural Abundance

Where this element is most commonly found in nature.

Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.

Appearance

The description of the element in its natural form.

Uses / Interesting Facts

Image explanation

The element and its alloys are used in the manufacture of valves and boiler plates.

Appearance

A silvery metal produced and sold as a grey powder and used in alloys, catalysts and electrodes. World production is 80,000 tonnes per year, most of which is converted to molybdenum sulfide, a lubricant additive. This element is essential for several living things, and probably for humans, although only in tiny amounts. The average human takes in about 0.3 grammes a day and stores about 5 milligrammes in the body

Uses

Molybdenum is a valuable alloying agent, as it contributes to the hardness and toughness of quenched and tempered steels. It is also used in certain nickel-based alloys which are heat-resistant and corrosion-resistant to chemical solutions. It has found use in electrical and nuclear applications, and as a catalyst in the refining of petroleum.

Biological role

Although it is toxic in anything other than small quantities, molybdenum is an essential element for animals and plants. If soil lacks this element the land is barren. Leguminous plants use the nitrogen-fixing enzyme nitrogenase, which contains molybdenum.

Natural abundance

The main source of this element is the ore molybdenite. Molybdenum can be obtained from this ore, but most commercial production is as a by-product of copper production.

Atomic Data Terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.

Electron affinity (kJ mol^-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *

Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, E_d in eV. χ_A - χ_B =(eV)-1/2sqrt(E_d(AB)-[E_d(AA)+E_d(BB)]/2), with χ_H set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).

1^st Ionisation energy (kJ mol^-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).

Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic Data

Atomic radius, non-bonded (Å)	2.170	Covalent radius (Å)	1.46
Electron affinity (kJ mol^-1)	72.146	Electronegativity (Pauling scale)	2.160
Ionisation energies (kJ mol^-1)	1^st 684.315 2^nd 1559.202 3^rd 2617.645 4^th 4476.916 5^th 5257.482 6^th 6640.849 7^th 12124.723 8^th 13855.283

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.

Key for numbers generated

Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9

Reserve base distribution

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)

Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)

Explanations for terminology

Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.

Sourced

The country with the largest reserve base.

Reserve Base Distribution

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.

Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.

Total Governance Factor

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.

Relative Supply Risk Index

The Crustal Abundance, Reserve Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply Risk

Scarcity factor	6.5
Country with largest reserve base	China, USA, Chile
Crustal abundance (ppm)	0.8
Leading producer	Mexico
Reserve base distribution (%)	43.70
Production concentration (%)	59.20
Total governance factor(production)	8

Top 3 countries (mined)	1) China, USA, Chile
Top 3 countries (production)	1) Mexico 2) China 3) USA

Oxidation states/ Isotopes

Key for Isotopes

Half Life
	y	years
	d	days
	h	hours
	m	minutes
	s	seconds
Mode of decay
	α	alpha particle emission
	β	negative beta (electron) emission
	β+	positron emission
	EC	orbital electron capture
	sf	spontaneous fission
	ββ	double beta emission
	ECEC	double orbital electron capture

Terminology

Common Oxidation states
The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.

Important Oxidation states
The most common oxidation states of an element in its compounds.

Oxidation States / Isotopes

Common oxidation states	6, 5, 4, 3, 2, 0
Isotopes	Isotope	Atomic mass	Natural abundance (%)	Half life	Mode of decay
	⁹²Mo	91.907	14.77	> 3 x 10¹⁷ y	β+-EC
	⁹⁴Mo	93.905	9.23	-	-
	⁹⁵Mo	94.906	15.9	-	-
	⁹⁶Mo	95.905	16.68	-	-
	⁹⁷Mo	96.906	9.56	-	-
	⁹⁸Mo	97.905	24.19	-	-
	¹⁰⁰Mo	99.907	9.67	6 x 10²⁰ y	β-β-

Pressure and Temperature - Advanced Terminology

Molar Heat Capacity (J mol^-1 K^-1)

Molar heat capacity is the energy required to heat a mole of a substance by 1 K.

Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, it provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.

Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour Pressure (Pa)

Vapour pressure is the measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure / Temperature - Advanced

Molar heat capacity
(J mol^-1 K^-1)

24.06

Young's modulus (GPa)

Unknown

Shear modulus (GPa)

Unknown

Bulk modulus (GPa)

231

Vapour pressure

Temperature (K)

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

Pressure (Pa)

1.83
x 10^-9

4.07
x 10^-7

3.03
x 10^-5

1.02
x 10^-3

1.89
x 10^-2

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History

Elements and Periodic Table History

The soft black mineral molybdenite (molybdenum sulfide, MoS₂), looks very like graphite and was assumed to be a lead ore until 1778 when Carl Scheele analysed it and showed it was neither lead nor graphite, although he didn’t identify it.

Others speculated that it contained a new element but it proved difficult to reduce it to a metal. It could be converted to an oxide which, when added to water, formed an acid we now know as molybdic acid, H₂MoO₄, but the metal itself remained elusive.

Scheele passed the problem over to Peter Jacob Hjelm. He ground molybdic acid and carbon together in linseed oil to form a paste, heated this to red heat in and produced molybdenum metal. The new element was announced in the autumn of 1781.

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Podcasts

Listen to Molybdenum Podcast

Transcript :

Chemistry in its element - molybdenum

Promo)

You're listening to Chemistry in its Element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry

(End promo)

Meera Senthilingam

This week, we clarify the importance of the often misunderstood molybdenum. Here's Quentin Cooper:

Quentin Cooper

The answer to the ultimate question - of life, the Universe and Everything - is, as every Douglas Adams fan knows, 42. And 42, as every Mendeleev fan knows, is the atomic number of molybdenum. And for many that - plus the indisputable fact that molybdenum is a funny word - is often about as far as their knowledge goes of this silvery metal - not that they'd have known it was a silvery metal - which is wedged between its better known brethren chromium and tungsten in group six of the periodic table. That odd-sounding name comes in a convoluted way from the Greek for lead, as ores of the two were often mixed up by early mineralogists - it was also frequently mistaken for graphite - and it wasn't until 1778 that molybdenum was recognised as a distinct entity deserving its own place in the periodic table, and a few years later still that it was finally isolated. The key breakthrough came from the Swedish chemist Carl Wilhlelm Scheele, better known as 'Hard luck Scheele' because he made a whole series of chemical discoveries, including oxygen, only for others to go and get the credit.

So its mistaken-identity history, its miscredited discoverer, its misleading and often mis-spelled name, all add to the aura of comedy and confusion around molybdenum.....and yet it's an element that's right at the root of life - not just human life, but pretty much all life on the planet: yes you'll find tiny amounts of it in everything from the filaments of electric heaters to missiles to protective coatings in boilers, and its high performance at high temperatures mean it has a range of commercial applications: it's useful in toughening up steel and giving it more corrosion resistance, as a catalyst in processes such as refining petroleum, and above all it's turned to when you need things to get hot but stay slippy - where WD40 and other petroleum derived oils are at risk of igniting, molybdenum sulfides are the basis of a range of lubricants which can cope with the heat and keep things moving smoothly.

But for all the ways we've discovered to use it, of far greater significance - although involving far smaller quantities of molybdenum - is the way we've evolved to make use of it within us. It's found in dozens of enzymes... including all important nitrogenase, which allows the most abundant element in the atmosphere, nitrogen, to be taken up and turned into compounds that enable bacteria, plants, us and everything between to synthesise and utilise proteins. Without proteins there wouldn't be much at all in the way of life....and without molybdenum there wouldn't be much at all in the way of proteins. And it turns up in other key human enzymes too such as xanthine oxidase in the liver, which is vital to our waste processing.

But just in case anyone's thinking of rushing off to buy one of the many commercially available trace mineral supplements with molybdenum it's worth adding that although like much of life on Earth we definitely need it.... we don't need that much of it: about a third of a gram is all you'll get through in an entire lifetime. That's next to nothing...but without it we'd be next to nothingness.

So, time to stop laughing at the funny name... molybdenum really is one of life's few true essentials.

Meera Senthilingham

So time to give some much-owed respect, it seems, to the element molybdenum. That was science broadcaster Quentin Cooper with the widely applied chemistry of molybdenum. Now, next week, blink and you may miss it.

Brian Clegg

If elements were insects, darmstadtium would be the mayfly of the chemical world. It exists for the most fleeting time before it transforms to something else. Darmstadium is never going to have a practical use - but its sheer brevity of existence gives it a wistful fascination.

Meera Senthilingham

And to find out what does happen in darmstadtium's brief existence on earth, in next week's Chemistry in its element. Until then, I'm Meera Senthilingham and thank you for listening.

(Promo)

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists dot com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld dot org forward slash elements.

(End promo)

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Video

Click here to view videos about Molybdenum

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Resources

Chromium, molybdenum and tungsten

Description :

In this experiment you will be looking at a group of transition elements chromium, molybdenum and tungsten.

AfL: Transition metal complexes

Description :

Assessment for Learning is an effective way of actively involving students in their learning. This is a series of plans based around chemistry topics.

A Spectacular Reversible Reaction

Description :

When concentrated hydrochloric acid is added to a very dilute solution of copper sulfate, the pale blue solution slowly turns yellow-green on the formation of a copper chloride complex. When concentra...

The transition elements

Description :

The purpose of this experiment is to examine some of the solution chemistry of the transition elements

Hexaaqua ion maps

Description :

This is a 'drag and drop' activity which uses an embedded macro that allows objects to be re-organised on a PowerPoint slide whilst in 'show' mode. Incomplete aqueous transition metal ion reaction seq...

Reactions of transition elements

Description :

The purpose of this experiment is to observe and interpret some of the chemistry of three first row transition elements and to compare them with a typical s-block element.

More resources related to Molybdenum...

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References

Images: Visual Elements © Murray Robertson 2011
Mining and Sourcing data: British Geological Survey – natural environment research council.
Text: John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.

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